Save the files pst-abspos.sty|tex in a directory,
which is part of your local TeX tree.
Then do not forget to run texhash to update this tree.
For more information see the documentation of your LaTeX distribution
on installing packages into your local TeX system or read the
TeX Frequently Asked Questions:
(http://www.tex.ac.uk/cgi-bin/texfaq2html?label=instpackages).